Work in the precast industry inevitably involves a requirement or specification established by one of many associations with acronyms such as ASTM, ACI and CSA.1 This series introduces you to these associations and their histories and a perspective on why they matter to precasters. This article takes a close look at AASHTO (for the ASTM profile, see the January-February 2011 issue of Precast Inc. magazine).

What is AASHTO?
AASHTO is the American Association of State Highway and Transportation Officials. It is a nonprofit, nonpartisan association representing highway and transportation departments in the United States and Puerto Rico. It represents five transportation modes: air, highways, public transportation, rail and water. Its primary goal is to foster the development, operation and maintenance of an integrated national transportation system.

Membership in AASHTO is on an agency basis and is not extended to individuals or private sector entities. All state Departments of Transportation are active members, as are several substate and federal transportation agencies in the United States. Many transportation agencies in other countries belong to the association as associate (non-voting) members.

Much of AASHTO’s work is done by committees comprised of member-department personnel who serve voluntarily. The association provides a forum for consideration of transportation issues and is frequently called upon by the U.S. Congress to conduct surveys, provide data and testify on transportation legislation (though a non-government body). Through AASHTO’s policy development activities, member departments often address federal programs and provide guidance.
AASHTO has developed a strategic plan to include the following goals:

Re-establish transportation as a national priority.

Advocate and communicate to achieve AASHTO’s goals.

Provide world-class technical services.

Assist state DOTs with leadership and performance.

The Highway Subcommittee on Bridges and Structures (SCOBS), in conjunction with many other committees and subcommittees, is working hard to meet Goal 3. The primary intent of this goal is to attain a world leadership role in the development of transportation standards and other technical services. This goal will focus on: increasing the number of beneficiaries; ensuring continued state DOT participation in critical technical activities; expanding training opportunities for transportation agency professionals; and developing centers of excellence in safety, operations, finance and freight transportation. As part of this goal, SCOBS, along with the Subcommittee on Maintenance, is striving to provide technical expertise, research and technical services in the area of preservation for the nation’s aging bridges and highway structures.

How AASHTO came to be
It all began in November 1914 when 14 state highway engineers met at the Georgian Terrace Hotel in Atlanta to discuss the creation of an association that would address the unique concerns of the public officials responsible for “getting America out of the mud.” They agreed to form the American Association of State Highway Officials (AASHO) as a forum to address highway issues and to promote state priorities at the national level. The engineers also called on all their colleagues to attend the new association’s first official meeting the following month in Washington, D.C.

That meeting in the U.S. Capitol, held Dec. 12 at the Raleigh Hotel, did much to set the tone for the association’s voice, vision and values in the decades since. This can be seen in AASHO’s first formal action at that meeting. Under the leadership of its first president, Henry Shirley of Maryland, the participants approved a legislative proposal authorizing participation of the federal government in highway construction. That proposal, subsequently presented to the U.S. Congress, laid the groundwork for the historic Federal Aid Highway Act of 1916.

Since then, the association has worked to strengthen and sustain the national highway and transportation system. These efforts have included the advocacy of other landmark federal legislation from the act that launched the Interstate Highway System in 1956 to the still-pending reauthorization of the Transportation Equity Act for the 21st Century. Other AASHTO milestones include:

Production of standards and specifications for highway design, construction and safety

Establishment of uniform symbols for road maps

Creation of nationwide route numbering of the primary U.S. highways and the National System of Interstate and Defense Highways (commonly called The Interstate System)

Coordination of such key research efforts as the AASHO Road Test in the 1950s and sponsorship of the National Cooperative Highway Research Program

Formation of a materials reference laboratory program

Development of computer software programs to facilitate highway and bridge analysis, design and construction management

The focus of the association evolved from highway-only to its present-day oversight of virtually all forms of transportation (air, rail, water, and public transportation). This happened after various federal agencies were brought together under the U.S. Department of Transportation, and state governments followed suit with similar reorganization. AASHO, recognizing and appreciating the increasingly multifaceted role of its member departments, became the American Association of State Highway and Transportation Officials (AASHTO) in 1973.

Standard specifications for highway bridges
For many years, precast manufacturers of underground products used designs that complied with either AASHTO HS20-44 or Alternate Military Loading (Interstate Loading), whichever standard correlated to the worst condition that could be applied to the structure.

The document titled “Standard Specifications for Highway Bridges” has for many years defined the load and design requirements for underground precast and cast-in-place concrete structures. The recommendations from this document are included in ASTM specifications written for underground precast concrete structures such as C478, C890, C913, C1443 and C1557.

The most recent version of the “Standard Specifications for Highway Bridges” is the 17th edition, published in 2002. The design methods in those 17 editions included the Allowable Stress Design (ASD) and Load Factor Design (LFD).

As the Interstate Highway System evolved in the 1950s, one of its goals was to transport military vehicles. The Alternative Military Load (also known as Interstate Load) was created to cover axle loads from heavy military equipment.

There was some concern during the end of the 20th century that the HS20 truck load rating did not adequately reflect actual conditions. As a result, some engineers have required an “HS25” truck load rating for underground precast structures. This rating has been interpreted as being 25% higher than the HS20 truck load. Thus, the HS20 axle load of 32,000 pounds (14,515 kg) becomes an HS25 axle load of 40,000 pounds (18,144 kg). The increased load can, in some cases, create the need for additional reinforcing steel and a thicker top slab on underground structures installed in areas exposed to heavy truck loads.

LRFD
At the 1993 annual meeting of the Bridges and Structures Subcommittee (SCOBS), member departments voted 41 to 5 to adopt the new AASHTO Load and Resistance Factor Design (LRFD) Bridge Specifications. In 1994, AASHTO published the first edition of LRFD in both standard and metric units. In anticipation of changes during the early years of LRFD, AASHTO and Federal Highway Administration voted to fund National Cooperative Highway Research Program to provide maintenance and enhancements to LRFD. LRFD is based on new developments in bridge engineering, sound principles and a logical approach to ensure constructability, safety, serviceability, inspectability, economy and aesthetics. The LRFD philosophy is consistent with other major bridge design codes adopted or being developed in Asia, Canada, Europe and other parts of the world.

Subsequent to the development of the new LRFD specifications, FHWA announced that all state bridge projects using federal funding must use the new and superior code. The implementation date for the switch to LRFD was set for Oct. 31, 2007. As a result, precast concrete manufacturers are seeing contract documents that require AASHTO HL93 truck loads, which is a new load designation under the LRFD.

Standard specifications for transportation materials and methods of sampling and testing
AASHTO publishes another set of specifications that precasters may often reference in manufacturing and quality control of their products: the Standard Specifications for Transportation Materials and Methods of Sampling and Testing. The latest version is the 30th edition and contains 414 material specifications and test methods commonly used in the construction of highway facilities, including 10 new and 69 updated specifications and test methods.

These specifications have been developed and maintained by transportation departments through participation in AASHTO’s Subcommittee on Materials. Many of the specifications that are pertinent to precast concrete have equivalencies in ASTM. Not all of the corresponding standards specific to various precast products (manholes, pipe, box culverts and others) are listed here (visit www.precast.org for more information).

and paste it into the corresponding place in the editor. Hide

Table ID:

The current (8th) edition of the NPCA QC Manual makes reference to AASHTO T277, the Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration, which serves as a good permeability indicator.

For precasters who manufacture products that are part of transportation projects (such as manholes, pipe, box culverts, stormwater structures, utility vaults, traffic barriers, and retaining and sound walls), an awareness of the background and purpose of AASHTO standards helps to emphasize the importance of manufacturing specification-compliant, quality precast concrete products.